Plasmonic Antireflection Coating for Photoconductive Terahertz Generation

Plasmon-enhanced photoconductive antennas allow for improved performance, particularly in below-band-gap absorption devices using low-temperature-grown GaAs. Here we design the plasmonic nanostructures to act as antireflection coatings as well, achieving below 10% reflection at 1570 nm wavelength in an optimized device. Quantitative agreement is seen between experiment and theory. Terahertz emission field amplitudes demonstrate 18 times enhancement compared to that of a conventional terahertz photoconductive antenna on the same substrate.